For the past several decades, high quality loudspeakers for studio monitoring as well as domestic use have been designed and optimized for use in a traditional two-channel stereophonic setup. When optimizing the timbre of such loudspeakers, the primary objective is to improve the perceived reproduction quality of voices and musical instruments at the center of the stereo image, right between the loudspeakers, where the solo singer or instrument is usually located. This perceived location improvement is obtained simply by feeding the source signal to both stereo loudspeakers simultaneously at an identical level and phase. We will call this reproduction channel the phantom center channel.
When switching from stereophonic to multi-channel audio, the phantom center channel is usually replaced by a physical center channel: A loudspeaker located straight in front of the listener. This was originally maintained when extending cinema systems from monophonic to stereophonic format for the purpose of ensuring correct localization of the movie dialog for all seats in the theatre. Via home cinema systems, such a loudspeaker arrangement has now been standardized for multi-channel audio as well (according to ITU-R Recommendation BS.775-1, “Multi-channel Stereophonic Sound Systems with and without Accompanying Picture”, International Telecommunication Union, Geneva, Switzerland, 1992-1994). Also, the use of a physical center channel in audio-only systems will make the stereo image less sensitive to variations in the listener's position.
However, as the music industry gained experience with this new reproduction format, one problem became apparent: many highly esteemed music producers decided not to use the physical center channel at all, thus discarding its beneficial stabilizing effect on the stereo image.
It is the object of this invention to provide a solution which will make the use of the physical center channel attractive.